import java.util.TreeMap;
public class Trie {

    private class Node{
        public boolean isWord; //到当前节点是否为一个单词
        public TreeMap<Character,Node> next;

        public Node(boolean isWord) {
            this.isWord = isWord;
            next = new TreeMap<>();
        }

        public Node(){
            this(false);
        }
    }

    private Node root;
    private int size;//存储单词数量

    public Trie(){
        root = new Node();
        size = 0;
    }

    //获得Trie中存储单词数量
    public int getSize(){
        return size;
    }
    //向Trie中添加一个新的单词
    public void add(String word){
        Node cur = root;
        for (int i = 0 ; i < word.length() ; i++) {
            char c = word.charAt(i);
            if (cur.next.get(c)==null)
                cur.next.put(c, new Node());
            cur = cur.next.get(c);
        }
        //此时cur在word的最后一个字母的位置
        //需要判断这个单词之前在不在Trie中，在的话，size++是不需要执行的
        if (!cur.isWord) {
            cur.isWord = true;
            size++;
        }
    }

    // 查询单词word是否在Trie中
    public boolean contains(String word) {
        Node cur = root;
        for (int i = 0 ; i < word.length() ; i++) {
            char c = word.charAt(i);
            if (cur.next.get(c) == null)
                return false;
            cur = cur.next.get(c);
        }
        return cur.isWord;
    }

    //查询是否在Trie中有单词以prefix为前缀
    public boolean isPrefix(String prefix) {
        Node cur = root;
        for (int i = 0 ; i < prefix.length() ; i++) {
            char c = prefix.charAt(i);
            if (cur.next.get(c) == null)
                return false;
            cur = cur.next.get(c);
        }
        return true;
    }
}




























